A rapid scanning microspectrophotometer has been designed and constructed which allows absorption spectra to be measured between 350 and 650 nm at a speed of 0.6 msec per wavelength band (10 nm). Experiments on frog (Rana pipens) have been performed or are in progress to measure the effects of several variables on visual pigment (rhodopsin) kinetic changes. These variables include pH, availability of glucose and oxygen, temperature, divalent cations, presence and absence of pigment epithelium and degree of attachment of rod outer segments. The results have confirmed the importance of pH in determining the rhodopsin photoproduct pathways and kinetics. For the first time, however, the metabolic and respiratory status of the retina can be paramount in determining photoproduct characteristics.